What is Silica and is it Bad for You?
When is dust not simply dust?
When it's made of crystalline silica. Then it's a hazardous material regulated by the Occupational Safety and Health Administration (OSHA).
What is Silica?
Silica is the common name for silicon dioxide (SiO2), a mineral that makes up 59% of the earth's crust by mass. You can find it in soil, sand, granite, concrete, and more than 95% of known rocks on the planet.
It comes in two forms: crystalline and non-crystalline (also called amorphous).
Crystalline silica is the most dangerous form. It's extremely useful for industrial and manufacturing purposes because it's hard, chemically inert, and has a high melting point. Crystalline silica is most commonly found as quartz, but also comes in the forms of cristobalite and tridymite.
You find non-crystalline silica in silica gel, silicone, and silicon carbide. These materials have much less potential to become a health hazard.
Respirable Crystalline Silica Safety Awareness Course: Construction
Learn about the health hazards of silica dust and how to protect yourself.
Respirable Crystilline Silica Safety Awareness Course: General Industry
Learn to prevent health issues caused by crystalline silica dust.
Is Silica Bad For You?
In its natural form, it's not.
Silica in rocks, soil, and sand are harmless. In fact, it's found naturally in soil and therefore many vegetables and grains. After we eat foods with silica, it's part of our own tissues. You might even see it in a dietary supplement or food additive.
The problem doesn't start until we begin to work with materials containing crystalline silica. Once crystalline silica becomes ground into dust, it goes airborne and it's small enough for people to inhale – 100 times smaller than natural sand particles.
This is called respirable crystalline silica (RCS). RCS is what poses a threat to your health.
Why is Silica Dust Bad for Your Health?
Breathing silica dust can put you at risk for a whole host of respiratory diseases from breathing tiny particles deep into your lungs.
It can also set off an immune reaction that damages other tissues or organs. As a result, there is some evidence that silica dust exposure causes kidney failure, rheumatoid arthritis, and other autoimmune conditions.
However, its relationship to lung diseases like silicosis is much more well-studied.
What is Silicosis?
Silicosis is the most common disease that results from silicate exposure.
We've known about silicosis for a long time. In the 1700s, an early medical scholar noted that when he autopsied stonecutters, their lungs contained large amounts of "sand." Modern pathologists say that silicosis can make lungs rock hard and impossible to cut with a scalpel.
Silicosis is as bad as it looks. You can contract it after just a few months of high exposure, but it's progressive. Your lungs form scar tissue in response to silica dust, and that keeps you from taking in enough oxygen.
There is no cure for silicosis. It can lead to disability and death.
What Other Respiratory Diseases Do You Get from Silica Exposure?
Research has led multiple global health organizations to classify crystalline silica as a known human carcinogen. There is strong evidence that you're more likely to get lung cancer with silicate exposure.
Respirable crystalline silica can also cause chronic obstructive pulmonary disease (COPD), increase your risk of contracting tuberculosis, and is associated with other serious lung diseases.
Where Does Silica Come From?
Respirable crystalline silica is created by cutting, chipping, grinding, drilling, or crushing any material that contains quartz, cristobalite, tridymite, or other forms of crystalline silica.
Since almost all material extracted from the earth's crust contains crystalline silica, that's a lot of potential opportunities to create silica dust.
Who is at Risk for Silicate Exposure?
According to OSHA, around 2.3 million U.S. workers are exposed to crystalline silica on the job. The vast majority of those workers (an estimated 80 to 90%) are in the construction industry these days, but others work in maritime, manufacturing, and hydraulic fracturing settings.
However, not all of those workers have a high risk of silica dust exposure. Particular job responsibilities put you in the most danger, including tasks like:
- Abrasive blasting (ie, sandblasting)
- Underground Mining
- Quarry work
- Foundry work
- Stoneware clay (ie, ceramics and pottery) production
- Glass production
- Cement, concrete, asphalt, and brick production
An estimated 100,000 U.S. workers fall under the high-risk category.
How Can You Prevent Silica Dust Exposure?
Employers can reduce silica dust exposure entirely by using safer substitutes for crystalline silica materials whenever possible.
If you have to work with crystalline silica, the most effective solution is to control silica dust at the source. Water spraying is often the best option for dust control. You need a fine mist directed at the point where you're cutting and grinding to keep silica dust from going airborne. The more water you use, the better the dust control.
When water isn't practical, other methods like vacuuming or ventilation should be used to control the amount of silica dust in the air.
You should also consider isolating the dust-producing activity from nearby workers (with a tent, for example). This puts the worker(s) inside the enclosure at a higher exposure risk, so it has to be combined with active ventilation and a filter sock to collect silica dust.
Finally, if you can't control silica dust at the source well enough, respirators can be used to protect workers from breathing it in.
What Are OSHA's Silica Standards?
OSHA updated its silica standards in 2016 to reflect current science about silica dust exposure and to require employers to use engineering controls (like the dust control measures described above).
The complete silica standards can be found under 29 CFR 1910.1053 for general industry and maritime workplaces and under § 1926.1153 for construction industry workplaces.
What Do the New OSHA Silica Standards Require?
As part of the change, they set new permissible exposure limits (PELs) for silica. The new PELs are universal – they apply to general industry, maritime, and construction workplaces alike.
Previously, requirements were much stricter for general industry. Maritime and construction workers had less protection.
Employers are now required to:
- Limit access to areas where you can be exposed above PELs.
- Restrict housekeeping practices that expose workers to silica.
- Take precautions that keep silica dust at or below PELs. Employers must try to solve the problem with engineering controls and work practices first – these are the dust control methods we described above.
- Provide respirators if exposure levels remain too high after dust control methods.
- Create a written exposure control plan.
- Offer medical exams every 3 years, including chest x-rays and lung function tests, to certain high-risk workers.
- Keep records of workers' silica exposure and medical exam results.
- Train workers on the health effects of silica exposure, what workplace tasks cause exposure, and how to protect themselves.
OSHA estimates that the new rules – particularly engineering control requirements – will prevent 600 deaths (and more than 900 new cases of silicosis) per year.
How are Silica Monitoring Standards Different For Construction Than Other Industries?
In addition to all of the above, employers that operate under maritime and general industry standards must conduct exposure assessments. That means they have to take air samples for silica and have them analyzed by qualified laboratories to make sure concentrations stay within PELs.
The rules are a little different for construction industry employers. OSHA created flexible compliance options for construction because exposure monitoring is impractical for some employers (and PELs change quickly when working outdoors).
OSHA provides construction employers with a list of common construction tasks that generate high RSC exposure. This list (Table 1) specifies the engineering controls, work practices, and respiratory protection that will effectively protect workers while they perform each task.
Any construction industry employer who fully and properly implements Table 1 is exempt from measuring exposure levels. Otherwise, they have to use air monitoring and lab assessments just like maritime and general industry employers.
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